Objective: To evaluate whether quantitative susceptibility mapping (QSM)-based substantia nigra (SN) volumetry improves differentiation of progressive supranuclear palsy (PSP) from Parkinson’s disease (PD) and multiple system atrophy (MSA) when combined with conventional T1-weighted MRI volumetry.

Background: PSP is a rare atypical parkinsonian syndrome often misdiagnosed as Parkinson’s disease (PD). Differentiation from multiple system atrophy (MSA) remains challenging because of overlapping clinical and imaging features. Although midbrain atrophy on MRI is a known PSP marker, its specificity is limited because similar changes may occur in MSA. We hypothesized that QSM-based substantia nigra (SN) volumetry may provide a more PSP-specific marker.

Method: We retrospectively analyzed PD (n=123), MSA (n=48), and PSP (n=22) patients. T1-weighted MRI underwent atlas-based volumetry of brainstem and ventricular regions. QSM images were reconstructed using a standard pipeline, and the SN was segmented using manual delineation assisted by an in-house U-Net model. SN volume, mean susceptibility, and susceptibility-to-volume ratio (SVR) were calculated. Group comparisons used age-adjusted analyses and Mann–Whitney U tests. Diagnostic performance was evaluated using receiver operating characteristic analysis and leave-one-out cross-validated logistic regression models.

Results: Midbrain volume was the best T1-based marker for differentiating PSP from PD (AUC=0.82, 95% CI 0.70–0.92), but showed limited discrimination between PSP and MSA (AUC=0.66, 95% CI 0.51–0.80). Among QSM-derived measures, SN volume showed strong discrimination of PSP from both PD (AUC=0.82, 95% CI 0.72–0.91) and MSA (AUC=0.81, 95% CI 0.69–0.91). The susceptibility-to-volume ratio (SVR) demonstrated even higher performance for differentiating PSP from PD (AUC=0.87, 95% CI 0.76–0.95) and also distinguished PSP from MSA (AUC=0.79, 95% CI 0.66–0.89). While pons volume alone differentiated PSP from MSA with an AUC of 0.78 (95% CI 0.66–0.88), combining pons volume with SN SVR improved diagnostic performance (AUC=0.88, 95% CI 0.78–0.95).

Conclusion: QSM-based SN volumetry complements conventional MRI. SN volume and SVR improve discrimination of PSP from PD and MSA and may enhance MRI-based differential diagnosis of parkinsonian syndromes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/qsm-based-substantia-nigra-volumetry-improves-differentiation-of-progressive-supranuclear-palsy-from-parkinsons-disease-and-multiple-system-atrophy/